Process for the dimerization of olefins

ABSTRACT

A process for the dimerization of alpha-alkenes having 2 to 12 carbon atoms in the presence of an alkanediol solvent and of a novel catalytic system formed by combining: 
     (a) a palladium(II) compound, 
     (b) a chelate ligand comprising a compound containing at least two N coordinating atoms which are connected through a chain comprising two C atoms, &gt;2.0 mol chelate ligand per gram-atom Pd being used, 
     (c) a protonic acid, except hydrohalogenic acids, and 
     (d) a salt of Cu, Fe, Zn, Sn, Mn, V, Al or a Group VIB metal, except a halide.

FIELD OF THE INVENTION

The invention relates to a process for the dimerization in the liquidphase of an alpha-alkene having in the range of from 2 to 12 carbonatoms per molecule. The invention also relates to a novel catalyticsystem.

BACKGROUND OF THE INVENTION

It is known from European Patent Application No. 170,311 to dimerize analpha-alkene having in the range of from 2 to 12 carbon atoms permolecule in the presence of a catalytic system formed by combining, inthe presence of water, an alcohol, or a carboxylic acid:

(a) a palladium(II) compound,

(b) a chelate ligand comprising a compound containing as coordinatingatoms at least two nitrogen atoms which are connected through a chaincomprising two carbon atoms, and

(c) a compound containing an anion of an acid, with the exception ofhydrohalogenic acids.

The reaction mixture obtained by means of this known process maycomprise a two-phase liquid system: a liquid dimer phase and a liquidsolvent phase containing the catalytic system. Both phases can easily beseparated by means of mechanical separation and the separated solventphase containing the catalytic system can be used for dimerizing furtherquantities of alpha-alkenes.

It has been observed that the dimer phase contains a portion of thechelate ligand and the solvent phase has a correspondingly reducedcontent thereof. This reduced content of chelate ligand may lower thecatalytic activity of the catalytic system, particularly whenconsiderably less than 2 mol of chelate ligand per gram-atom ofpalladium(II) remains.

Starting this known process by using more than 2 mol of the chelateligand per gram-atom of palladium(II) would compensate for said loss ofchelate ligand, but renders the catalyst less active.

A novel catalytic system has now been found that is surprisingly activewhen more than 2 mol of the chelate ligand per gram-atom of palladiumare used.

SUMMARY OF THE INVENTION

This invention provides a process for the dimerization in the liquidphase of an alpha-alkene having in the range of from 2 to 12 carbonatoms per molecule in which the dimerization is carried out in thepresence of an alkanediol solvent and of a catalytic system formed bycombining:

(a) a palladium(II) compound,

(b) a chelate ligand comprising a compound containing as coordinatingatoms at least two nitrogen atoms which are connected through a chaincomprising two carbon atoms, more than 2.0 mol of the chelate ligand pergram-atom of palladium(II) being used,

(c) a protonic acid, with the exception of a hydrohalogenic acid, and

(d) a salt of copper, iron, zinc, tin, manganese, vanadium, aluminium orof a metal of Group VIB of the Periodic Table of the Elements, with theexception of a halide.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

It has been found that the presence of both the protonic acid and saidsalts has a synergistic effect on the activity of the catalytic systemvis-a-vis the presence of the protonic acid alone and of said saltsalone. Simultaneously, a very high selectivity to dimers, usually higherthan 95%, has been observed. The selectivity to dimers is defined as themolar percentage of dimers in the product formed.

Alpa-alkenes having in the range of from 2 to 12 carbon atoms which canbe used in the process according to the present invention may be linearor branched, such as, for example, ethene, propene, 1-butene, 1-pentene,1-hexene, 5-methyl-1-hexene, 1-octene and 1-dodecene. The preferredalpha-alkenes are ethene, propene and 1-butene.

The word "dimerization" as it is used herein, refers to the reaction oftwo identical olefins as well as the reaction of two different olefins.An example of the latter reaction is that between ethene and propene, orbetween propene and 1-butene.

According to the invention, both homogeneous and heterogeneous catalyticsystems can be used. The use of homogeneous catalytic systems ispreferred. Palladium(II) compounds which can be used in the processaccording to the invention therefore preferably comprise palladium(II)compounds which are soluble in the reaction medium or form in-situsoluble compounds therein. Examples of suitable palladium(II) compoundsare palladium nitrate, palladium sulfate and palladium carboxylates,preferably carboxylates of carboxylic acids having not more than 12carbon atoms per molecule. Palladium alkanoates, in particular palladiumacetate, are preferably used.

Further examples of suitable palladium compounds are palladium complexessuch as bis(2,4-pentanedionato)palladium, bis(picolinato)palladium,tetrakis(triphenylphosphine)palladium, tetrakisacetonitrile palladiumtetrafluoroborate, bis(tri-o-tolylphosphine)palladium acetate,bis(triphenylphosphine)palladium sulfate, palladium olefin complexes andpalladium-hydride complexes. A mixture of palladium(II) compounds may bepresent in the catalytic system.

The quantity of the palladium compound used may vary within wide rangesand is generally in the range between 10⁻⁶ and 10⁻¹ gram-atom palladiumper mol olefin starting material. A range between 10⁻⁵ and 10⁻²gram-atom palladium compound is preferred.

Preference is given to chelate ligands containing in the molecule agroup of the formula ##STR1## wherein the dotted line represents severalkekule resonance structures in case of condensed aromatic ring systemsas e.g. occurring in 1,10-phenanthroline. For example,N,N'-1,2-ethanediylidenebisphenylamine,N,N'-1,2-ethanediylidenebis[4-chlorophenylamine],N,N'-1,2-ethanediylidenebis[4-methoxyphenylamine], N-substitutedderivatives of 2-pyridinemethanimine, 2,2'-bipyridyl,4,4'-dimethyl-2,2'-bipyridyl, 4,4'-dichloro-2,2'-bipyridyl,4,4'-dimethoxy-2,2'-bipyridyl, 1,10-phenanthroline,5-chloro-1,10-phenanthroline, 4,7-diphenyl-1,10-phenanthroline,4,7-dimethyl-1,10-phenanthroline, 2,9-dichloro-1,10-phenanthroline,1,10-phenanthroline-5-sulfonic acid and salts thereof,4,7-diphenyl-1,10-phenanthrolinedisulfonic acid and salts thereof, and3,5-cyclohexadiene-1,2-diimine may be used.

The compounds preferably used in the catalytic system used in theprocess according to the invention are 1,10-phenanthroline or aderivative thereof and 2,2'-bipyridyl or a derivative thereof. Mostpreferred is 1,10-phenanthroline.

A mixture of chelate ligands such as, for example, a mixture of1,10-phenanthroline and 2,2'-bipyridyl can be used.

The quantity of chelate ligand used in the catalytic system is at least2.0 mol per gram-atom of palladium(II) and is preferably in the range offrom 2.5 to 25 mol per gram-atom palladium(II).

Any protonic acid, with the exception of hydrohalogenic acids, and anysalt of a protonic acid and derived from copper, iron, zinc, tin,manganese, vanadium, aluminum or of a Group VIB metal, with theexception of a halide, may be present. The acid and salt preferably havea non-coordinating anion, by which is meant that little or no covalentinteraction takes place between the palladium(II) and the anion. Typicalexamples of such anions are PF₆ ⁻, SbF₆ ⁻, BF₄ ⁻ and ClO₄ ⁻.

The protonic acid and the acid from which the salt is derived preferablyhave a pKa of less than 3 and, more preferably, less than 2, measured inaqueous solution at a temperature of 18° C.

Preferred protonic acids are sulfonic acids and acids that can beformed, possibly in-situ, by interacting a Lewis acid such as, forexample, BF₃, AsF₅, SbF₅, PF₅, TaF₅ or NbF₅ with a Broensted acid suchas, for example, a hydrohalogenic acid, in particular HF, fluorosulfonicacid, phosphoric acid or sulfuric acid. Specific examples of acids ofthe latter type are fluorosilicic acid, HBF₄, HPF₆ and HSbF₆. Examplesof suitable sulfonic acids are fluorosulfonic acid and chlorosulfonicacid and the hereinafter specified sulfonic acids.

A preferred group of protonic acids has the general formula I: ##STR2##wherein Z represents sulfur or chlorine and, if Z is chlorine, Rrepresents oxygen and, if Z is sulfur, R represents an OH group or anhydrocarbon group. As used herein, the term "hydrocarbon group" refersto hydrocarbon groups which can be either unsubstituted or substituted,with the substituent being any substituent which does not interfere withthe reaction.

When the hereinbefore-stated protonic acids are used in the processaccording to the invention, the anions of the compounds can beconsidered to be non-coordinating.

The substituted or unsubstituted hydrocarbon group represented by R ispreferably an alkyl, aryl, aralkyl or alkaryl group having 1 to 30, inparticular 1 to 14, carbon atoms. The hydrocarbon group may, forexample, be substituted with the halogen atoms, in particular, fluorineatoms. Examples of suitable acids of the general formula I areperchloric acid, sulfuric acid, 2-hydroxypropane-2-sulfonic acid,benzenesulfonic acid, 1- and 2-naphthalenesulfonic acid,p-toluenesulfonic acid and trifluoromethanesulfonic acid, the last twoacids being the most preferred.

Examples of suitable carboxylic acids are formic acid, acetic acid,monochloroacetic acid, dichloroacetic acid, trichloroacetic acid and,preferably, trifluoroacetic acid.

A mixture of protonic acids may be present in the catalytic system.

Among the salts that are present preference is given to copper and ironsalts, such salts imparting a very high activity to the catalyticsystem. Among the Group VIB metals, chromium is preferred.

A mixture of two or more of the metals may be present such as, forexample, copper and iron, or, copper and vanadium.

Among the salts, sulfates, p-tosylates and tetrafluoroborates arepreferred. Very good results have been obtained with sulfates andp-tosylates. The protonic acid and the salt may have the same ordifferent anions. For example, a mixture of p-toluenesulfonic acid and asulphate may be used.

The protonic acid and the salt are preferably used in a total quantityin the range of from 0.01 to 150 and in particular 1 to 100 equivalentsper gram-atom palladium.

The amount of protonic acid which is used per equivalent of salt is notcritical and may vary within wide ranges. Preferably, in the range offrom 0.1 to 10 equivalents of the protonic acid per equivalent of saidsalt is used. However, amounts of less than 0.1 and more than 10equivalents are not excluded.

It will be appreciated that when the catalytic system applied in theprocess according to the invention is formed by combining in-situ therequired ingredients, a palladium complex compound with catalyticactivity may be formed in the reaction mixture. An example of such acompound is palladium bis(1,10-phenanthroline)diperchlorate orditosylate. The use of such a palladium complex compound when preparedseparately as a catalytic system is within the scope of the presentinvention.

In the process of the invention, the catalytic system is used in thepresence of an alkanediol solvent. Very good results have been obtainedwith ethylene glycol. Other examples of suitable alkanediol solvents are1,2-propanediol, 1,3-propanediol, 1,4-butanediol, 1,2-butanediol,1,6-hexanediol and polyethylene glycols such as diethylene glycol. Thepresence of a co-solvent is not excluded. Examples of co-solvents arealcohols, carboxylic acids and water. The alcohols or carboxylic acidsmay be aliphatic, cycloaliphatic or aromatic and may be substituted withone or more substituents, for example alkoxy, cyano or ester groups orhalogen atoms. The alcohols or carboxylic acids preferably contain notmore than 20 carbon atoms per molecule. Examples of suitable alcoholsare methanol, ethanol, propanol, isobutyl alcohol, tertiary butylalcohol, stearyl alcohol, benzyl alcohol, cyclohexanol, allyl alcoholand chlorocapryl alcohol.

Further examples of co-solvents are hydrocarbons such as, for example,hexane and in particular aromatic hydrocarbons such as benzene ortoluene; halogenated hydrocarbons such as chloroform, chlorobenzene orperfluoroalkanes; ketones such as acetone, diethyl ketone or methylisobutyl ketone; ethers such as tetrahydrofuran, dimethyl ether ofdiethylene glycol (also referred to as "diglyme"), methyl t-butyl etheror 1,4-dioxane; sulfones such as dimethyl sulfone, methyl butyl sulfone,tetrahydrothiophene 1,1-dioxide (also referred to as "sulfolane"), andsulfoxides such as dimethyl sulfoxide or diethyl sulfoxide.

The process according to the present invention can be carried out attemperatures of up to 200° C. and preferably in the range between 20° C.and 135° C. The pressure preferably lies between 1 and 100, inparticular between 20 and 75, bar gauge.

The process according to the invention can be carried out batchwise,semi-continuously or continuously. The reaction time may vary inrelation to the temperature used, between 0.5 and 20 hours.

The dimers may be isolated from the reaction mixture obtained in anysuitable manner, for example by mechanically separating the reactionmixture into a liquid dimer phase and a liquid solvent phase. The liquiddimer phase may then be separated by distillation. The dimers aresuitable as a feedstock for hydroformylation processes wherein an alkeneor a mixture of alkenes is reacted with hydrogen and carbon monoxide inthe presence of a hydroformylation catalyst, to produce aldehydes and/oralcohols. Where the product is mainly aldehyde a separate hydrogenationis required to form alcohols. The products obtained by the processaccording to the present invention require only distillation to separateunconverted mono-olefin and heavy ends before use in a hydroformylationprocess.

The invention further provides a novel catalytic system formed bycombining:

(a) a palladium(II) compound,

(b) a chelate ligand comprising a compound containing as coordinatingatoms at least two nitrogen atoms which are connected through a chaincomprising two carbon atoms, more than 2.0 mol of the chelate ligand pergram-atom of palladium(II) being used,

(c) a protonic acid, with the exception of a hydrohalogenic acid, and

(d) a salt of copper, iron, zinc, tin, manganese, vanadium, aluminium orof a metal of Group VIB of the Periodic Table of the Elements, with theexception of a halide.

The following Examples are intended to further illustrate the inventionand are not to be construed as limiting the scope of the invention. Inall Examples, the hexenes formed had a linearity of about 60%.

EXAMPLES 1-9

A 300 ml magnetically stirred Hastelloy C autoclave ("Hastelloy" is atrade mark) was charged with ethylene glycol (50 ml), palladium(II)acetate (0.5 mmol), 1,10-phenanthroline (2 mmol) and p-toluenesulfonicacid (2 mmol). In each of these nine examples, the autoclave was alsocharged with a salt, as detailed in Table 1 hereinafter. This table alsoshows the amounts in which these salts were used. The autoclave was thenflushed with propene, charged with 50 ml of liquid propene and heated toa temperature of 80° C. After the reaction time indicated in Table 1,the contents of the autoclave were analyzed by gas/liquidchromatography.

Table 1 presents the conversion of propene and the selectivity tohexenes. The selectivity to nonenes is the difference between 100% andthe selectivity to hexenes.

                  TABLE 1                                                         ______________________________________                                        Ex-              mmol           Con-   Selectivity,                           am-              of      Reaction                                                                             version,                                                                             %,                                     ple  Salt        salt    time, h                                                                              %      to hexenes                             ______________________________________                                        1    Cu(p-tosylate).sub.2                                                                      0.5     5      70     88.2                                   2    Cu(p-tosylate).sub.2                                                                      1.0     1      85     96.6                                   3    FeSO.sub.4  1.0     1      85     95.3                                   4    Cr.sub.2 (SO.sub.4).sub.3                                                                  0.67   2      75     96.4                                   5    ZnSO.sub.4  0.5     2      75     96                                     6    SnSO.sub.4  1.0     2      75     96.4                                   7    MnSO.sub.4  1.0     2      65     97.3                                   8    VOSO.sub.4  1.0     1      60     97                                     9    Al.sub.2 (SO.sub.4).sub.3                                                                  0.67   2      40     98.7                                   ______________________________________                                    

EXAMPLE 10

Example 2 was repeated with the difference that the temperature was 75°C. instead of 80° C. The conversion of propene was 80% after 5 hours andthe selectivities to hexenes and nonenes were 86.7% and 13.3%,respectively.

COMPARATIVE EXPERIMENT A

Example 2 was repeated with the difference that copper(p-tosylate)₂ wasnot present and that 4 mmol instead of 2 mmol of p-toluenesulfonic acidwas used.

After 5 hours a conversion of propene of only 10% was observed.

COMPARATIVE EXPERIMENT B

Example 2 was repeated with the difference that p-toluenesulfonic acidwas not present and that 2.0 mmol instead of 1.0 mmol ofcopper(p-tosylate)₂ was used.

After 5 hours a conversion of propene of only 35% was observed.Prolonging the reaction time beyond 5 hours did not further increase theconversion.

COMPARATIVE EXPERIMENT C

Example 2 was repeated with the difference that Zr(SO₄)₂ (1 mmol)instead of Cu(p-tosylate)₂ (1.0 mmol) was used.

After 5 hours a propene conversion of only 10% was observed.

COMPARATIVE EXPERIMENT D

Example 2 was repeated with the difference that UO₂ SO₄ (1 mmol) insteadof Cu(p-tosylate)₂ (1.0 mmol) was used.

The conversion of propene was less than 5% after 5 hours.

COMPARATIVE EXPERIMENT E

Example 3 was repeated with the difference that p-toluenesulfonic acid(2 mmol) was not present and that 2 mmol FeSO₄ instead of 1 mmol FeSO₄was present.

The conversion of propene was less than 5% after 5 hours.

COMPARATIVE EXPERIMENT F

Example 3 was repeated with the difference that NiSO₄ (1.0 mmol) insteadof FeSO₄ (1.0 mmol) was present.

The conversion of propene was less than 10% after 5 hours.

I claim:
 1. A process for the dimerization in the liquid phase of analpha-alkene which comprises contacting an alpha-alkene having in therange of from 2 to 12 carbon atoms per molecule with an alkanediolsolvent in the presence of a catalytic system formed by combining:(a) apalladium(II) compound, (b) a chelate ligand comprising a compoundcontaining as coordinating atoms at least two nitrogen atoms which areconnected through a chain comprising two carbon atoms, wherein more thanabout 2.0 mol of said chelate ligand per gram-atom of palladium(II) isused, (c) a protonic acid, with the exception of a hydrohalogenic acid,and (d) a salt of a protonic acid selected from the group consisting ofcopper, iron, zinc, tin, manganese, vanadium, aluminum, a metal of GroupVIB of the Periodic Table of the Elements and mixtures thereof, with theexception of a halide.
 2. The process of claim 1 wherein said metal ofGroup VIB is chromium.
 3. The process of claim 1 wherein a copper saltis used.
 4. The process of claim 1 wherein an iron salt is used.
 5. Theprocess of claim 1 wherein said protonic acid and said protonic acidfrom which said salt is derived have a pKa of less than 3, measured inaqueous solution at a temperature of 18° C.
 6. The process of claim 1wherein said protonic acid and said salt have a non-coordinating anion.7. The process of claim 1 wherein said protonic acid and said protonicacid from which said salt is derived is an acid of the general formula I##STR3## wherein Z represents sulfur or chlorine and, if Z is chlorine,R represents oxygen and, if Z is sulfur, R represents an OH group or ahydrocarbon group.
 8. The process of claim 7 wherein said hydrocarbongroup R is selected from the group consisting of an alkyl, aryl, aralkylor alkaryl group having from 1 to about 30 carbon atoms.
 9. The processof claim 8 wherein said acid of the general formula I isp-toluenesulfonic acid.
 10. The process of claim 1 wherein said salt isa sulfate.
 11. The process of claim 1 whrein said salt is atetrafluoroborate.
 12. The process claim 1 wherein said chelate ligandcomprises a compound containing in the molecule a group of the formula##STR4## wherein the dotted line represents several kekule resonancestructures in case of condensed aromatic ring systems.
 13. The processof claim 12 wherein said chelate ligand comprises 1,10-phenanthroline ora derivative thereof.
 14. The process of claim 12 wherein said chelateligand comprises 2,2'-bipyridyl or a derivative thereof.
 15. The processof claim 1 wherein said chelate ligand is used in an amount in the rangeof from about 2.5 to about 25 mol per gram-atom palladium(II).
 16. Theprocess of claim 1 wherein said the protonic acid and said salt are usedin a total quantity in the range of from 1 to 100 equivalents pergram-atom palladium.
 17. The process of claim 1 wherein in the range offrom about 0.1 to about 10 equivalents of said protonic acid perequivalent of said salt are used.
 18. The process of claim 1 wherein thealkanediol solvent is ethylene glycol.